Unrelated crazy idea:
Fighting Styles
You can learn one style and an additional number of styles equal to your Intelligence modifier. (I would go so far as to indicate with INT 8 you won't get a style, but I am an evil, cruel, and wicked DM.

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Since many styles don't have crazy synergies, I don't think this would be too OP on the surface, and it would give at least some benefit for Fighters, Paladins, and Rangers to have a decent INT score. With adding UA styles, you have a decent selection even for someone like a Fighter/Wizard (bladesinger).
Any big issues with this? At a glance I don't see any.